The forced-convective heat transfer to supercritical helium has been investigated. The test section is a 1.25mm I.D., 200mm long vertical straight tube through which helium flows upward or downward and heated uniformly. The conditions covered are inlet fluid temperature between 4.7 and 10.8K, system pressures of 0.3, 0.5 and 0.8MPa, mass velocities of 20, 40 and 80kg/(m2·s) and heat fluxes of 500, 1000, 2000 and 4000W/m2. Experimental results on the distribution of wall temperature and heat transfer coefficient are presented. A comparison of the experimental results between upward and downward flow directions and discussion about the differences between them, in the light of the buoyancy effect, are done.
